Abstract
The simultaneous operation of multiple different semiconducting metal oxide (MOX) gas sensors is demanding for the readout circuitry. The challenge results from the strongly varying signal intensities of the various sensor types to the target gas. While some sensors change their resistance only slightly, other types can react with a resistive change over a range of several decades. Therefore, a suitable readout circuit has to be able to capture all these resistive variations, requiring it to have a very large dynamic range. This work presents a compact embedded system that provides a full, high range input interface (readout and heater management) for MOX sensor operation. The system is modular and consists of a central mainboard that holds up to eight sensor-modules, each capable of supporting up to two MOX sensors, therefore supporting a total maximum of 16 different sensors. Its wide input range is archived using the resistance-to-time measurement method. The system is solely built with commercial off-the-shelf components and tested over a range spanning from 100 Ω to 5 GΩ (9.7 decades) with an average measurement error of 0.27% and a maximum error of 2.11%. The heater management uses a well-tested power-circuit and supports multiple modes of operation, hence enabling the system to be used in highly automated measurement applications. The experimental part of this work presents the results of an exemplary screening of 16 sensors, which was performed to evaluate the system’s performance.
Highlights
Metal Oxide (MOX) gas sensors are cheap, easy to manufacture, and have become an economic success in many applications such as gas leak detection or air quality monitoring [1].Research projects have shown that commercially available sensors can be used for the detection of substances other than those they were originally designed to detect [2].In such scenarios, the sensors resistive output can, depending on the target gas and sensor material, have a dynamic range of several decades
Considering that this work’s main contribution is situated in the field of complete interfaces for MOX gas sensors and MOX sensor arrays comprising sensor readout and heater management, we investigated the approaches that have been used and proposed by other research teams
The continuous measurement is started by configuring the range, and the first measurement is triggered by providing the integration signal (CONV) to the DDC112
Summary
Dynamic Range Readout and Heater Management for Semiconducting Metal Oxide Gas Sensors.
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